Cooling of internal combustion engines

ABSTRACT

An engine assembly (10) for a propeller-driven aircraft is disclosed, the assembly including an engine (11), a drive shaft (13) driven by the engine (11), and a radiator (20) comprising an aperture (24) for receiving the drive shaft (13), the aperture (24) being located such that the radiator (20) substantially circumferentially surrounds the drive shaft (13). The aperture (24) may take various forms, such as a hole within the interior of the radiator (20) or a blind slit formed within the radiator (20).

CLAIM OF PRIORITY

This application is a continuation of and claims priority under 35U.S.C. § 371 to International Application No. PCT/EP2014/061446 filed onJun. 3, 2014, which in turn claims priority to European App. No.13175982.1 filed on Jul. 10, 2013, the contents of which areincorporated herein by reference for all purposes.

TECHNICAL FIELD

This invention relates to cooling of internal combustion engines, andparticularly but not exclusively to a radiator for cooling an internalcombustion engine within a propeller aircraft.

BACKGROUND

Internal combustion engines are widely used in virtually all types ofpowered vehicles, including automobiles, motorcycles, boats andaircraft. A major problem with internal combustion engines is thegeneration of waste heat, which must be efficiently transferred from theengine to the surroundings in order to avoid heat-related engine failuresuch as cracking, warping or degradation of the engine lubrication oil.

There are two common engine cooling techniques: air cooling and liquidcooling. Whilst air cooling was popular during the infancy of combustionengines, it is no longer widely used; liquid cooling is now the favouredcooling technique for most combustion engines.

Air cooling involves directing air, typically at a high velocity, aroundthe engine cylinder or cylinder block. Fins or other formations aretypically provided on the outer surface of the cylinder or cylinderblock in order to increase the surface area and hence enhance heattransfer.

In liquid cooling, the transfer of heat from the engine to thesurroundings is via an intermediary liquid cooling circuit. A liquidcoolant is passed through fluid passages defined within or around theengine cylinder or cylinder block, whereupon heat generated during theinternal combustion process is transferred to the coolant. The coolantis then passed to a heat exchanger, commonly known as a radiator, havinga large surface area exposed to the surroundings. As the coolantcirculates through the radiator, heat is transferred from the liquidcoolant to the surroundings. The cold coolant subsequently exits theradiator and is fed back to the engine cylinder or cylinder block torepeat the process. Alternatively, in an open circuit, the cooling fluidthat exits the radiator may be disposed of and fresh cooling fluid fedto the engine cylinder or cylinder block.

In general, the liquid coolant utilised in liquid-cooling devices iswater based but may comprise other agents such as antifreeze and/orcorrosion inhibitors.

A cooling technique similar to the above-described liquid cooling mayalso be employed in relation to the engine lubricating oil. Cooling ofthe engine-lubricating oil is commonly known as “oil cooling” andcomprises passing the engine oil from the engine to its own dedicatedradiator and subsequently returning the oil to the engine. Oil coolingis generally employed in conjunction with one of the above-describedair-cooling and liquid-cooling techniques i.e. the engine oil istypically not the principal coolant.

In order for liquid cooling and oil cooling to constitute effectiveengine cooling techniques, there must be efficient heat transfer fromthe radiator to the surroundings. In practice, this is achieved byproviding the radiator with an array of fins or other formations inorder to increase the surface area thereof, and by generating a highvelocity air flow around and/or though the radiator.

One known technique for generating an air flow around or through aradiator is to rely on ram-air pressure provided by the forward motionof the vehicle. In such arrangements, air intakes are provided at thefront of the vehicle and air received through these intakes is directedtowards the radiator. However, one problem with this arrangement is thatthe cooling air flow is only generated when the vehicle is in motion.This can lead to overheating of the engine when engine is operationalbut the vehicle is stationary, for example when an aircraft is on theground ready for take-off.

It is also known to direct air towards the radiator via one or morefans. The power required to operate the fans must, however, be providedby the engine, thereby increasing the total engine load and hencecontributing to the heating of the engine. In view of the fact that thefans are provided for the sole purpose of cooling the engine, theside-effect of heating the engine represents a considerable failing in afan-based engine cooling arrangement.

Definitions

The term “radiator” is used herein to include any form of heat exchangerand is not restricted to a particular form or mode of heat transfer. Forexample, the heat exchangers used in known engine cooling systems areencompassed within the term “radiator” in spite of the fact that theheat transfer is predominantly via convection and conduction as opposedto radiation.

The term “aperture” is used herein to include a hole, a slot, a gap, aslit, an indentation or any other form of opening.

Statement of Invention

In accordance with the present invention, as seen from a first aspect,there is provided an engine assembly for an aircraft, the assemblycomprising:

-   -   an internal combustion engine;    -   a drive shaft configured to be driven by the engine;    -   a radiator comprising an aperture through which the drive shaft        is received, the aperture being located such that the radiator        substantially circumferentially surrounds the drive shaft.

One advantage of the present invention is that distance between theradiator and the engine is reduced in comparison to known engineassemblies. Accordingly, fluid lines between the engine and the radiatorare short and direct, if such lines are required at all. This providesthe benefits of reduced cost, reduced weight, a simplified installationand a reduced risk of leaks.

Preferably the radiator circumferentially surrounds at least 70% of thedrive shaft. In other words, a radial line drawn from the longitudinalaxis of the drive shaft intersects the radiator over at least 70% of thepossible 360 degree azimuthal angular range.

More preferably, the radiator circumferentially surrounds at least 90%of the drive shaft. Yet more preferably, the radiator circumferentiallysurrounds 100% of the drive shaft.

The radiator may be arranged for cooling a coolant fluid that has beenheated by the engine prior to passing to the radiator. In thisembodiment, the engine assembly may comprise one or more fluid passageswithin or proximal to the engine, the fluid passages being fluidlycoupled to the radiator such that the coolant fluid passes from thefluid passages to the radiator.

Alternatively, the radiator may be arranged for cooling enginelubricating oil that is passed to the radiator from the engine.

The aperture preferably comprises a hole located within an interior ofthe radiator such that the radiator circumferentially surrounds thedrive shaft. Preferably the radiator is substantially annular, theaperture preferably defining the centre of the annulus.

Alternatively, the aperture may comprise a blind slit that extends froman outer peripheral edge of the radiator to an interior of the radiator.Preferably the radiator is substantially circular in cross-section, theslit preferably extending radially from an outer peripheral edge of theradiator to a centre-point of the radiator.

Alternatively, the aperture may comprise a gap that extends from anouter peripheral edge of the radiator to an opposing outer peripheraledge of the radiator such that the aperture separates the radiator intotwo disconnected portions. Preferably each portion of the radiator issubstantially semi-circular in cross-section.

The drive shaft may be coupled to a crank shaft of the engine.Alternatively, the propeller shaft may be received in a rotor of arotary engine such as a Wankel engine.

The drive shaft is preferably arranged for rotating a propeller.Preferably a proximal end of the drive shaft is coupled to the engineand a distal end of the drive shaft is coupled to the propeller.Advantageously, the location of the radiator between the engine andpropeller provides a compact and light weight installation. Furthermore,the rotary action of the propeller assists the air flow around and/orthrough the radiator. It has been found by the applicants that the airflow provided by the rotation of the propeller is greater than thatwhich may be achieved by relying on the ram-air pressure that isprovided by the forward motion of the air vehicle. Furthermore, thepropeller generates an air flow even when the engine is running whilstthe aircraft is stationary on the ground.

The radiator may comprise a first substantially planar surface arrangedto extend in a plane substantially perpendicular to the longitudinalaxis of the drive shaft such that the normal to the surface issubstantially parallel to the longitudinal axis of the drive shaft. Theradiator may further comprise a second substantially planar surfacearranged to extend in a plane substantially perpendicular to thelongitudinal axis of the drive shaft.

The first surface is preferably proximal to the propeller and the secondsurface is preferably proximal to the engine when the drive shaft isreceived in the aperture of the radiator.

Preferably the first and second surfaces are substantially circular.

The radiator may comprise additional apertures for allowing air to passtherethrough. One advantage of this arrangement is that the surface areaof the radiator is increased by virtue of the apertures, therebyimproving the efficiency of cooling of the radiator.

The radiator may comprise a substantially planar backing member, whichpreferably abuts the second surface of the radiator. It is envisagedthat a planar backing member will be particularly appropriate toembodiments in which the aperture comprises a blind slit or a gap. Inthese embodiments, the backing member is preferably located at least atthe circumferential locations not encompassed by the radiator. Incertain embodiments, the backing member may be elongate and arranged tocover an outer portion of the blind slit or both outer portions of thegap, leaving only a central hole through which the drive shaft may bereceived. In an alternative embodiment, the backing member may haveouter dimensions substantially identical to the second surface of theradiator such that the backing member extends to the periphery of theradiator, the backing member preferably comprising a hole located withinan interior the backing member through which the drive shaft isreceived.

The additional apertures may extend longitudinally through the radiatorbetween the first and second surfaces, each aperture thereby defining anelongate passage. The elongate passage may comprise a restricted portionat a substantially longitudinally central position. One advantage ofproviding a restricted portion is that the velocity of the air isincreased at said portion, thereby improving the efficiency of coolingof the radiator. It is thought that this effect will be particularlyprevalent when the radiator is located behind the propeller blades andhence receives air that has been accelerated by the rotary action of thepropeller blades.

In one embodiment, the radiator is formed of a plurality ofsubstantially parallel elongate tubular elements arranged for conveyingcooling fluid, air passages being defined between adjacent elements.

The backing member may comprise apertures at locations corresponding tothe locations of the additional apertures provided in the radiator,thereby permitting air to pass through both the radiator and the backingmember and hence provide effective cooling of the radiator.

Preferably the radiator comprises a shroud, the shroud preferablycomprising a tubular side wall having a longitudinal axis substantiallyparallel to the longitudinal axis of the drive shaft. More preferablythe longitudinal axis of the tubular side wall of the shroud iscollinear with the longitudinal axis of the drive shaft. The shroud ispreferably arranged to circumferentially surround the drive shaft and atleast an inner portion of the radiator.

The tubular side wall of the shroud is preferably upstanding from thefirst surface of the radiator. More preferably, the tubular side wall ofthe shroud is upstanding from an outer peripheral edge of the firstsurface of the radiator.

The shroud may be substantially cylindrical. Alternatively, the tubularside wall of the shroud may flare outwardly, for example the shroud maybe frustro-conical.

An air intake for the engine may be provided proximal to a peripheraledge of the radiator.

In accordance with the present invention, as seen from a second aspect,there is provided a radiator for an aircraft, the radiator comprising:

-   -   an aperture for receiving a drive shaft, the aperture being        located such that the radiator substantially circumferentially        surrounds the drive shaft when the drive shaft is received in        the aperture; and,    -   a longitudinally extending shroud comprising a tubular side wall        arranged to circumferentially surround the drive shaft when the        drive shaft when the drive shaft is received in the aperture.

The aperture and/or the shroud may be as hereinbefore described.

In accordance with the present invention, as seen from a third aspect,there is provided a method of cooling an engine arranged for driving apropeller, the method comprising:

-   -   installing a radiator as hereinbefore described such that the        radiator substantially circumferentially surrounds a drive shaft        of the engine;    -   fluidly connecting the radiator such that the radiator receives        fluid that has been heated by the engine.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described by way ofexample only and with reference to the accompanying drawings, in which:

FIG. 1(a) is a side view of an engine assembly in accordance with anembodiment of the present invention;

FIG. 1(b) is a perspective view of the engine assembly of FIG. 1(a);

FIG. 2 is an exploded perspective view of the radiator of the engineassembly illustrated in FIGS. 1(a) and 1(b);

FIG. 3 is a perspective view of an alternative embodiment of a radiatorsuitable for use within the engine assembly illustrated in FIGS. 1(a)and 1(b); and,

FIG. 4 is a flow diagram of a method of cooling an engine arranged fordriving a propeller in accordance with an embodiment of the presentinvention.

Referring to FIGS. 1(a), 1(b) and 2 of the drawings, there isillustrated an engine assembly 10. The engine assembly 10 forms part ofa propeller aircraft (not shown). It is envisaged that the engineassembly 10 will be housed within a cowling (not shown) and locatedtowards the front of the aircraft.

The assembly 10 includes an internal combustion engine 11. The engine 11is supplied with air and fuel for combustion by means of an air intakeduct 12 and a fuel injector respectively. The air intake duct 12 isarranged to receive air from the front of the aircraft via an air inletaperture formed in the engine cowling.

The engine 11 is arranged for rotating a drive shaft 13. It is envisagedthat the engine 11 will be a Wankel engine, in which case a proximal endof the drive shaft 13 will be located within the rotor of the engine 11.A distal end of the drive shaft 13 is coupled to a propeller (not shown)located at the nose of the aircraft.

The assembly 10 further includes an engine cooling circuit forcirculating cooling fluid around the engine 11. The cooling circuitcomprises a pump (not shown) and a series of conduits (not shown)defined within or around the engine 11. The cooling circuit furthercomprises a radiator 20 mounted directly on the main engine body 11. Theposition of the radiator 20 proximal to the engine 11 minimises thetotal distance that must be spanned by the cooling circuit and henceprovides a reduced cost, reduced weight, a simplified installation and areduced risk of leaks. The radiator 20 is provided with an inlet 21 forreceiving cooling fluid from the conduits defined within or around theengine cylinder block. The radiator is also provided with an outlet 22for passing cooling fluid that has been cooled by the radiator to adownstream component in the engine cooling circuit. In certainembodiments, the cooling fluid that exits the radiator outlet 22 isimmediately returned to the conduits defined within or around the engine11 for absorption of heat generated by the engine 11.

The radiator 20 is formed of a plurality of spaced apart elongatetubular elements 23 arranged for conveying cooling fluid. Together, theplurality of tubular elements 23 provide the radiator 20 with asubstantially cylindrical shape, the radius of the radiator 20 beingsubstantially greater than the longitudinal length of the radiator 20.First and second manifolds (not shown) are provided at the respectiveends of the elongate tubular elements 23. In use, the cooling fluid thatenters the radiator 20 at the fluid inlet 22 is divided at the firstmanifold between each of the tubular elements 23. The cooling fluid thenpasses through the tubular elements 23 and is re-combined at the secondmanifold for subsequent passage out of the radiator 20. Theabove-described structure of spaced apart tubular elements 23 providesthe radiator 20 with a large surface area and therefore facilitatesefficient cooling thereof. Furthermore, the elongate spaces between thetubular elements 23 define air passages through the radiator 20, therebypermitting air to flow through the radiator 20 and hence enhancing theefficiency of cooling thereof.

An aperture 24 is formed in the radiator 20, though which the driveshaft 13 of the engine assembly extends. The location of the aperture 24in the centre of the radiator 20 permits the radiator 20 tocircumferentially surround the drive shaft 13. The dimensions of theaperture 24 are such that the drive shaft 13 fits within the aperture 24without making physical contact therewith but leaving minimal free spacetherebetween. In the illustrated embodiment, the aperture 24 is a squarehaving a side length marginally greater than the diameter of the driveshaft 13. In an alternative embodiment (not shown), the aperture may becircular and comprise a diameter marginally greater than the diameter ofthe drive shaft 13. The radiator may comprise a substantially planarbacking member 30, which preferably abuts the second surface of theradiator proximal to the engine 11. Backing member 30 may include a holethrough which the drive shaft 13 is received.

In certain embodiments, the radiator may be provided with alongitudinally extending shroud 25, as illustrated in FIG. 3. The shroud25 consists of a tubular side wall that extends from peripheral edge ofthe radiator 20. The tubular side wall of the shroud 25 thus constitutesan extension to the side wall of the radiator 20. The longitudinal axisof the tubular side wall of the shroud 25 is co-axial with thelongitudinal axis of the drive shaft (not shown in FIG. 3) such that theshroud 25 circumferentially surrounds the drive shaft. When thepropeller (not shown) is connected to the drive shaft, the end of thetubular side wall of the shroud distal from the radiator 20 is adjacentto the rear side of the propeller blades and marginally spaced aparttherefrom. It has been found by the applicants that a shroud such asthis enhances the air flow through the radiator 20 and hence improvesthe efficiency of engine cooling.

It will be appreciated that it is possible to retro-fit a radiator 20 asdescribed above to an existing engine assembly. With reference to FIG.4, retro-fitting the radiator 20 comprises installing the radiator 20around the drive shaft 13 at step 101. It is envisaged that the radiator20 will be installed in the position illustrated in FIGS. 1(a) and 1(b).The engine cooling circuit is then fully connected at step 102. Inparticular, fluid conduits formed within the engine 11 are connected tothe radiator 20.

Once the radiator 20 is installed and is operational, the pump of theengine cooling circuit pumps cooling fluid into the conduits defined inand around the engine 11, whereupon the cooling fluid absorbs heat fromthe engine 11 and thus cools the engine 11. The coolant fluid from theconduits is then passed to the inlet 21 of the radiator 20 andchannelled through the elongate tubular elements 23 of the radiator 20.The large surface area to volume ratio of each of the tubular elements23 provides effective cooling of the coolant fluid, which is then passedout of the radiator 20 via the fluid outlet 22.

The efficiency of cooling provided by the radiator 20 may be greatlyenhanced by energising the propeller. In particular, the location of theradiator 20 downstream of the propeller enables exploitation of the highvelocity air flow generated by the propeller.

The invention claimed is:
 1. An engine assembly for an aircraft, theassembly comprising: an engine; a drive shaft configured to be driven bythe engine, the drive shaft having a distal end; a bladed propellerlocated at the distal end of the drive shaft with respect to the engine;a radiator comprising an inlet that is substantially parallel to thedrive shaft and an aperture through which the drive shaft is received,the aperture being located such that the radiator substantiallycircumferentially surrounds the drive shaft, the radiator furthercomprising a longitudinally extending shroud, the longitudinallyextending shroud comprising a tubular side wall arranged tocircumferentially surround the drive shaft; characterized in that thetubular side wall of the longitudinally extending shroud extendsforwardly of the inlet and towards the bladed propeller from an outerperipheral edge of the radiator, and an end of the tubular side wall ofthe longitudinally extending shroud distal from the radiator is adjacentto the rear side of the propeller blades, whereby the cooling of theengine is improved.
 2. An engine assembly according to claim 1, whereinthe aperture comprises a hole located within an interior of the radiatorsuch that the radiator circumferentially surrounds the drive shaft. 3.An engine assembly according to claim 1 where the radiator is arrangedto circumferentially surround at least 90% of the drive shaft.
 4. Anengine assembly according to claim 1, wherein the drive shaft isarranged for rotating a propeller.
 5. An engine assembly according toclaim 1, wherein the radiator comprises additional apertures forallowing air to pass therethrough.
 6. An engine assembly according toclaim 1, further comprising a planar backing member arranged to abut asurface of the radiator proximal to the engine, the planar backingmember comprising a hole within an interior thereof through which thedrive shaft is received.
 7. A radiator for an aircraft, the radiatorincluding an inlet and comprising: an aperture for receiving a driveshaft, a propeller positioned on the drive shaft, the aperture beinglocated such that the radiator substantially circumferentially surroundsthe drive shaft when the drive shaft is received in the aperture; ashroud comprising a tubular side wall having a longitudinal axissubstantially parallel to the longitudinal axis of the drive shaft andthe inlet, the shroud arranged to circumferentially surround the driveshaft when the drive shaft is received in the aperture, characterized inthat the tubular side wall of the shroud extends from an outerperipheral edge of the radiator and forwardly of the inlet, the tubularside wall being closer to the propeller than the inlet, whereby theshroud improves the cooling of the engine.
 8. A method of cooling anengine arranged for driving a bladed propeller, the method comprising:installing a radiator comprising an inlet and an aperture for receivinga drive shaft, with a propeller upon the drive shaft, wherein the inletof the radiator is substantially parallel to the drive shaft and theradiator being installed such that the radiator substantiallycircumferentially surrounds the drive shaft; fluidly connecting theradiator such that the radiator receives fluid that has been heated bythe engine, mounting a longitudinally extending shroud comprising atubular side wall arranged to circumferentially surround the drive shafton the radiator, characterized in that the shroud is mounted to extendforwardly of the inlet and towards the bladed propeller from an outerperipheral edge of the radiator, and an end of the tubular side wall ofthe shroud distal from the radiator is adjacent to the rear side of thepropeller blades, such that the shroud enhances air flow through theradiator.